Hello Soulhunter
The bottom line is - some people are born healers and you seem to be one of them. It not necessarily reiki that you impart, there are many types of healing.
I would suggest that you turn to an experienced healer in the Native American tradition, to teach you how to protect yourself from absorbing other people's negativity, and to channel your ability for the best outcome.
In the meantime, before you attempt to heal again, try surrounding yourself with white protective light, and also make sure you ground yourself well. There is no necessity to drain yourself in the way you do - it's not beneficial to you or the recipient of your healing. Best of luck.